1. Field of the Invention
The present invention relates to a method for producing 3-amino-4-substituted-5-pyrazolones and more particularly to a method for producing 3-amino-4-substituted-5-pyrazolones useful as a coupler intermediate for photosensitive materials, or as an intermediate for color marking materials.
2. Description of the Related Art
A two-equivalent coupler for forming a magenta color image, which the two-equivalent coupler is a homopolymer or a copolymer including a repeating unit derived from an ethylenic unsaturated monomer including a pyrazolone residue, is particularly useful as a magenta color-forming coupler for color photography of a subtractive color system (see U.S. Pat. No. 4,367,282).
Such an ethylenic unsaturated monomer including a pyrazolone residue, providing the repeating unit of the polymer coupler, can be synthesized by a method which includes a step of introducing, in 4-position, a group releasable by a coupling reaction with the oxidant of developing agent (such a group hereinafter also called “coupling releasable group”), and which combines a residue having an ethylenic unsaturated group to an amino group in 3-position of a 3-amino-4-substituted-5-pyrazolone. The 3-amino-4-substituted-5-pyrazolone used as an intermediate has usually been synthesized, as indicated by the following reaction scheme by protecting the amino group in 3-position of a 3-amino-5-pyrazolone (A) which is a starting material with an acetyl group, halogenating 4-position of the resultant compound, introducing a coupling releasable group by substitution reaction of the halogen and removing the acetyl group (see J. of Synthetic Organic Chem. Japan, Vol. 45, No. 2, p. 151–161 (1987)).

A key step in the foregoing reaction scheme is a substitution step of obtaining a compound (D) from a compound (C). This step, however, has drawbacks of a very low yield and high incidence of by-products, due to inhomogenization of 4-halogenated material, generation of carbene (separation of a halogen atom with electron pairs from the 4-halogenated material resulting in generation of carbene), and subsequent by-reactions such as imerization/trimerization. Of the carbene. In order to avoid such as drawbacks, it has been reported that use of a benzoyl group for protecting the 3-amino group significantly improves the yield of the substitution step (see JP-A No. 62-70363). In such a method, acid hydrolysis is employed for de-protection of the benzoyl group.
However, de-protection of the benzoyl group by acid hydrolysis requires a higher temperature and a longer time than de-protection of the acetyl group, which cannot avoid by-reactions such as partial cleavage of the pyrazolone ring and increase in coloring component amount. As a result, when a polymer coupler synthesized from the compound obtained in this method is applied in a photosensitive material, photographic characteristics deteriorate.
In order to avoid drawbacks resulting from such a de-protection step, a method has been reported in which de-protection of the benzoyl group of a 3-benzoylamino-4-substituted-5-pyrazolone having the benzoylamino group in 3-position is conducted by alkali hydrolysis in the presence of a specified metal compound such as a barium compound or a lithium compound and neutralization of the reaction mixture with oxalic acid (see JP-A No. 2002-338548).
However, when producing on an industrial scale, the producing method described in JP-A No. 2002-338548 is not necessarily satisfactory in manipulating properties thereof and the like, and further improvements have been desired.
More specifically, according to investigations by the present inventors, improvements are required in processing of barium compound after execution of alkali hydrolysis and in ensuring the quality of 3-amino-4-substituted-5-pyrazolones to be obtained. These improvements become important particularly in mass production.
Since processed water used in the reaction contains a large amount of barium ions, and cannot be discharged as it is from the standpoint of maintaining a clean environment, it is necessary to remove the barium ions in some manner. In the method described in JP-A No. 2002-338548, the barium compound is treated with oxalic acid, but the resulting barium oxalate is extremely poor in fluidity and filterability of the reaction liquid and is unsuitable for mass production. As a result, such a barium compound remains in the obtained 3-amino-4-substituted-5-pyrazolones, resulting in deteriorated quality such as turbidity.
Also, when a reaction mixture is colored, it is effective to remove coloring components by extracting an aqueous phase containing a desired substance with an organic solvent. For such a purpose, extraction with an aliphatic halogenated organic solvent such as 1,2-dichloroethane is effective. However, because of recent concern regarding the detrimental influence of halogenated organic substances, particularly chlorinated compounds, on the environment, usage of organic solvents has been required which does not affect the environment.
As explained in the foregoing, prior production methods have not been advantageous in productivity, separation and purification of a desired product, time required for manufacture, and consideration on the environment, and there has been a strong desire for a technology capable of producing a large amount of highly pure 3-amino-4-substituted-5-pyrazolones through simple operations.
Thus, there has been a need for a method for producing, at a high yield, a highly pure 3-amino-4-substituted-5-pyrazolone which does not cause deterioration in photographic performance due to impurities, which method can be conducted economically on an industrial scale, with the environment taken into consideration, and with waste material reduced as much as possible.